1. Field of the Invention
The present invention relates to a light emitting module and a lamp device for vehicles including the same.
2. Description of the Related Art
In general, vehicles are equipped with lamp devices for illuminating nearby objects during poor lighting conditions or signaling the state of driving to nearby vehicles or pedestrians.
The lamp device for vehicles includes a head lamp mounted to the front side of the vehicle and a tail lamp mounted to the rear side of the vehicle. The head lamp is a lamp for illuminating the area ahead while driving at night. The tail lamp includes a brake lamp, which is turned on when a driver steps on a brake, and a turn signal lamp, which indicates the direction of travel of the vehicle.
Recently, light emitting diodes or laser diodes have been used as light sources for automotive lamp devices for good energy efficiency.
In particular, laser diodes are receiving attention due to their high degree of straightness, long-distance illumination and non-disturbance of the field of vision of drivers of oncoming vehicles.
The laser diode needs a phosphor and a lens assembly in order to output white light. However, this complicates the structure of the automotive lamp device, reduces efficiency, and increases the volume of the device. The lamp device for vehicles having a conventional laser diode will now be described.
FIG. 26 is a conceptual view of a conventional light emitting module. Referring to FIG. 21, a conventional light emitting module operates in such a manner that blue light generated from a laser diode is focused while passing through a prism 3 and a lens 4, the focused light is reflected from a first optical path conversion member 5, passes through a light transmissive phosphor 6 and is converted into white light, and the white light is radiated forward from a wavelength conversion unit 7.
However, if the light emitting module is arranged lengthwise along an optical axis inside the head lamp for vehicles, the length of the head lamp may be increased in response thereto.
Further, since the conventional light emitting module needs a relatively large number of components and has an optical path structure in which the light passes through each component only once, it may be hard to manufacture a compact head lamp due to the overall size of the components.
Specifically, light transmitted through the light transmissive phosphor 6 spreads out in a fan shape. For this reason, it is necessary for light incident upon the light transmissive phosphor 6 to be concentrated on a small spot (about 0.5 mm). The conventional light emitting module uses the above-described optical path in order to focus light (having a diameter of about 6 mm) emitted from the laser diode on a small spot on the light transmissive phosphor 6.
In addition, using a large number of components in order to focus light on such a small spot may increase costs and deteriorate reliability, and using the light transmissive phosphor may cause a decrease in efficiency.
The light transmissive phosphor must be configured such that light is transmitted through the front surface and the rear surface of the light transmissive phosphor, which have a large area than the side surface of the light transmissive phosphor, and heat is dissipated through the side surface of the light transmissive phosphor, through which light is not transmitted. As a result, a heat sink must be connected to the side surface of the light transmissive phosphor.
In this case, the contact area between the light transmissive phosphor and the heat sink is small with the result that heat is not easily dissipated from the light transmissive phosphor, whereby the light transmissive phosphor easily overheats. In general, the efficiency of the light transmissive phosphor is abruptly reduced at high temperature with the result that lighting using the light transmissive phosphor has limited intensity of light.
In addition, the relative position between a condensing lens and each light source is very important in order to condense light into a front space. A small spatial difference therebetween greatly may reduce the efficiency of light generated by the light emitting module. Furthermore, light may not be efficiently condensed into a space.
Meanwhile, in a head lamp for vehicles, which uses a blue laser as a light source, light is locally concentrated on the surface of a phosphor, with the result that the surface of the phosphor is heated to 200° C. or higher. In a case in which the phosphor is heated to a high temperature as described above, a conventional wavelength conversion device, which is formed of a silicon resin containing phosphor powder dispersed therein, may be destroyed by heat, or wavelength conversion efficiency may be extremely reduced.